The Siemens 3RT7027-1AG20 is a size S0 3-pole contactor from the SIRIUS family, rated for main circuit insulation voltage up to 690 V. It uses screw-type terminals on both the main and auxiliary/control circuits, so it's a direct fit for existing panel wiring practices that prefer screw clamping over spring-cage.
The auxiliary contact block is field-addable. Auxiliary contact ratings at 230 V are 6 A, at 400 V are 3 A, and at 690 V are 1 A — these are the continuous current limits for the built-in auxiliary contacts, not the main poles. The coil holding power is only 0.24 W DC, which keeps the control transformer load low in a multi-contactor panel. The front and terminal areas are both IP20 — finger-safe but not protected against water ingress, so it belongs inside a rated enclosure. For short-circuit coordination, with type 2 coordination required, use a gL/gG NH 3NA 50 A fuse; with type 1 coordination, a 125 A fuse. This matters when sizing upstream protection to avoid contactor damage during a fault.
Integration notes
Dimensions are 91 mm deep, 45 mm wide, 85.5 mm tall — the S0 footprint. The 45 mm width means it occupies two 22.5 mm module spaces on the DIN rail, standard for this frame size. The shock resistance is 12.5g for 5 ms and 7.8g for 10 ms sine pulse — robust enough for most industrial panel environments. Wire sizes accepted: 2x (0.5 to 1.5 mm²) solid/stranded and 2x (0.75 to 2.5 mm²) with ferrule, for both main and control circuits. The screw terminals are standard for North American and European panel builds.